Question: $ \left(\dfrac{81}{64}\right)^{-\frac{1}{2}}$
Solution: $= \left(\dfrac{64}{81}\right)^{\frac{1}{2}}$ Figure out what goes in the blank: $\Big(? \Big)^{2}=\dfrac{64}{81}$ Figure out what goes in the blank: $\Big({\dfrac{8}{9}}\Big)^{2}=\dfrac{64}{81}$ So $\left(\dfrac{81}{64}\right)^{-\frac{1}{2}}=\left(\dfrac{64}{81}\right)^{\frac{1}{2}}=\dfrac{8}{9}$